N = int(input())
x = [None] * N
y = [None] * N
for i in range(N):
    x[i], y[i] = map(int, input().split())

INF = 10 ** 12
burst = []
for i in range(N):
    for j in range(i + 1, N):
        res = (x[j] - x[i]) ** 2 + (y[j] - y[i]) ** 2
        burst.append((res, i, j))
burst.sort()

baloon = set()
cnt = 0
for b, i, j in burst:
    if i in baloon or j in baloon:
        continue
    if i == 0:
        cnt += 1
        baloon.add(j)
        continue
    else:
        baloon.add(i)
        baloon.add(j)
print(cnt)